In recent years, an optical image measuring technique of forming images that show the surface morphology and internal morphology of measured objects by using a light beam from a laser light source or the like has attracted attention. Unlike an X-ray CT apparatus, the optical image measuring technique is noninvasive to human bodies, and is therefore expected to be utilized more particularly in the medical field and biological field.
Japanese Unexamined Patent Application Publication No. Hei 11-325849 (Patent Document 1) discloses a device to which the optical image measuring technique is applied. This device has such a configuration that: a measuring arm scans an object by a rotary deflection mirror (a Galvano mirror); a reference arm is provided with a reference mirror; and an interferometer is mounted at the outlet to analyze, by a spectrometer, the intensity of an interference light of light fluxes from the measurement arm and the reference arm. Moreover, the reference arm is configured to gradually change the light flux phase of the reference light by discontinuous values.
The device of the Patent Document 1 uses a technique of so-called “Fourier Domain OCT (Optical Coherence Tomography).” That is to say, the device radiates a low-coherence light beam to a measured object, superposes the reflected light and the reference light to generate an interference light, and acquires the spectral intensity distribution of the interference light to execute Fourier transform, thereby imaging the morphology in the depth direction (the z-direction) of the measured object.
Furthermore, the device described in the Patent Document 1 is provided with a Galvano mirror that scans with a light beam (a signal light), and is thereby configured to form an image of a desired measurement target region of the measured object. Because this device is configured to scan with the light beam only in one direction (the x-direction) orthogonal to the z-direction, an image formed by this device is a two-dimensional tomographic image in the depth direction (the z-direction) along the scanning direction (the x-direction) of the light beam.
Japanese Unexamined Patent Application Publication No. 2002-139421 (Patent Document 2) discloses a technique of scanning with a signal light in the horizontal direction and the vertical direction to form a plurality of two-dimensional tomographic images in the horizontal direction, and acquiring and imaging three-dimensional tomographic information of a measured range based on the tomographic images. As the three-dimensional imaging, for example, a method of arranging and displaying a plurality of tomographic images in the vertical direction (referred to as stack data or the like), and a method of executing a rendering process on a plurality of tomographic images to form a three-dimensional image are considered.
Japanese Unexamined Patent Application Publication No. 2007-24677 (Patent Document 3) and Japanese Unexamined Patent Application Publication No. 2006-153838 (Patent Document 4) disclose other types of optical image measuring devices. The Patent Document 3 describes an optical image measuring device that images the morphology of a measured object by scanning the measured object with light of various wavelengths, acquiring the spectral intensity distribution based on an interference light obtained by superposing the reflected lights of the light of the respective wavelengths on the reference light, and executing Fourier transform. Such an optical image measuring device is called a Swept Source type or the like.
Further, the Patent Document 4 describes an optical image measuring device that radiates a light having a predetermined beam diameter to a measured object and analyzes the components of an interference light obtained by superposing the reflected light and the reference light, thereby forming an image of the measured object in a cross-section orthogonal to the travelling direction of the light. Such an optical image measuring device is called a full-field type, en-face type or the like.
Japanese Unexamined Patent Application Publication No. 2008-73099 (Patent Document 5) discloses a configuration in which the OCT technique is applied to the ophthalmologic field. Before the optical image measuring device was applied to the ophthalmologic field, a fundus oculi observing device such as a retinal camera had been used (for example, refer to Japanese Unexamined Patent Application Publication No. Hei 09-276232 (Patent Document 6)).
A fundus oculi imaging device using the OCT technique has a merit that a tomographic image and three-dimensional image of the fundus oculi can be acquired, as compared with a retinal camera that merely images the fundus oculi surface from the front. Therefore, contribution to increase of the diagnosis accuracy and early detection of a lesion is expected. Moreover, the application field of an optical image measuring device using this OCT technique has been extended to measurement use of various physical quantities of eyes such as the ocular axial length, the size of a lesion site and a chamber angle.
Consequently, in Japanese Unexamined Patent Application Publication No. 2007-37984 (Patent Document 7), an optical image measuring device that measures the axial length from the corneal reflection light and the fundus oculi reflection light and obtains OCT images of the anterior segment based on the reflection light of a signal light from the cornea and the reference light, or an optical image measuring device that measures the axial length from the corneal reflection light and the fundus oculi reflection light and obtains OCT images of the fundus oculi based on the reflection light of the signal light from the fundus oculi and the reference light are disclosed. That is, a technology that can measure axial lengths and obtain OCT images of the anterior segment or the fundus oculi with a single device is disclosed.
As described above, obtaining a variety of organism information of an eye with a single device is desired from the viewpoint of examination efficiency and particularly in recent years, a technology that can obtain both OCT images of the fundus oculis and anterior segments with a single optical image measuring device is anticipated.
However, with the optical image measuring device, when attempting to obtain a vivid tomographic image, a signal light is required to be efficiently focused on the depth zone of its image target. Generally, in the imaging optical system through which the signal light passes, the position on which the signal light is focused is fixed to one region and focus is blurred in other regions.
FIG. 13 is a diagram that shows part of a common imaging optical system. A signal light that exits from an end face 152b of an optical fiber 152a enters into a lens 142 and becomes a parallel light flux. This signal light that became the parallel light flux is then condensed to one region via a scan unit 141 that has a galvanometer mirror, etc., an imaging lens 126, a relay lens 125, a focusing lens 124, and an objective lens 113. When a working distance Wd such that the signal light condenses on a fundus oculi Ef of an eye E is matched with the distance between the objective lens 113 and a corneal vertex Ec, the anterior segment Ea is not focused.
Therefore, although a variety of organism information can be obtained as a vivid tomographic image from OCT images of the fundus oculi Ef shown in FIG. 14B, according to OCT images of the anterior segment Ea shown in FIG. 14A, because the corneal reflection light from the vertex Ec is of high intensity, it can be distinguished, but because distinguishing the other part such as a posterior surface of the cornea or crystalline lens is difficult, this organism information is almost impossible to obtain.
Consequently, for example, a photographing method in which after matching the working distance Wd such that the signal light is focused on the fundus oculi Ef of the eye E to the distance between the objective lens 113 and the corneal vertex Ec, an OCT image of the fundus oculi Ef is first obtained, then an OCT image of the anterior segment Ea is obtained after changing the distance between the objective lens 113 and the corneal vertex Ec to the working distance Wd such that the signal light is focused on the anterior segment Ea of the eye E, can be considered.
However, with this photographing method, because a total of two adjustments of the distance between the objective lens 113 and the corneal vertex Ec must be performed, the examination time becomes long and both the examiners and subject bear a large burden.
Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei 11-325849
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-139421
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2007-24677
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2006-153838
Patent Document 5: Japanese Unexamined Patent Application Publication No. 2008-73099
Patent Document 6: Japanese Unexamined Patent Application Publication No. Hei 09-276232
Patent Document 7: Japanese Unexamined Patent Application Publication No. 2007-37984